Ignition systems and strategies for internal combustion engines have a variety of different known forms, depending upon the design of the engine, the fuel type and combustion charge composition, and the operating environment. Spark-ignited systems are well known and widely used, perhaps most familiar from the gasoline engines commonly used in automobiles. Compression ignition systems are typically used in diesel engines, also applied to mobile vehicles as well as many other applications, particularly those that are heavy duty. For spark-ignited engines, an electrical spark provides a localized, high temperature ignition point for fuel and air to produce a flame that subsequently propagates throughout the cylinder. Compression ignition involves increasing the temperature and pressure of a mixture of fuel and air to an autoignition threshold, which can produce multiple different autoignition points within the cylinder. In either case, the end result is ignition and combustion of a charge of fuel and air that causes a rapid increase in pressure and temperature within the cylinder to drive linear motion of a piston. Both traditional spark-ignited and compression ignition systems can have various advantages or disadvantages depending upon the environment of application.
Another type of ignition system, also known for many years but receiving increased implementation and development efforts relatively more recently, is known as a prechamber ignition system. A prechamber ignition system involves the combustion of a relatively small amount of fuel, in a combustion prechamber that is in fluid communication or fluidly connectable to a main combustion chamber or cylinder in an internal combustion engine. Ignition and combustion of the relatively small amount of fuel in the prechamber, which can be the same fuel or a different fuel from the fuel forming a main charge, produces jets of hot, actively combusting fuel and air that penetrate into the main combustion chamber to ignite the main charge of fuel and air therein.
Prechamber ignition devices can provide a relatively robust mechanism for ignition, and can be relatively precisely controlled. With the advent of increasingly stringent emissions requirements in certain jurisdictions, prechamber ignition devices have been applied for the purpose of igniting relatively lean mixtures of fuel and air, commonly a gaseous fuel such as natural gas, that are less readily ignited by other techniques. Lean operation can provide for relatively low amounts of certain emissions. United States Patent Application Publication No. 2017/0074224 to Ge sets forth one design for a fuel admission valve for a prechamber ignition device.